"U.S. emissions of carbon dioxide related to energy use fell 2.8 percent last year, according to an estimate by the Energy Information Administration, driven down by high oil prices and the sagging economy. The drop in carbon dioxide emissions was the steepest since 1982.

The amount of carbon dioxide produced for every dollar of economic output also declined by 3.8 percent, the federal agency said, as industry and motorists became more efficient and frugal and as renewable energy sources gained a slightly larger share of the energy market. That was far greater than the average decline in carbon intensity in previous years."